The importance of plant genetic diversity (PGD) is now being recognized as a specific area since exploding population with urbanization and decreasing cultivable lands are the critical factors contributing to food insecurity in developing world. Agricultural scientists realized that PGD can be captured and stored in the form of plant genetic resources (PGR) such as gene bank, DNA library, and so forth, in the biorepository which preserve genetic material for long period. However, conserved PGR must be utilized for crop improvement in order to meet future global challenges in relation to food and nutritional security. This paper comprehensively reviews four important areas; (i) the significance of plant genetic diversity (PGD) and PGR especially on agriculturally important crops (mostly field crops); (ii) risk associated with narrowing the genetic base of current commercial cultivars and climate change; (iii) analysis of existing PGD analytical methods in pregenomic and genomic era; and (iv) modern tools available for PGD analysis in postgenomic era. This discussion benefits the plant scientist community in order to use the new methods and technology for better and rapid assessment, for utilization of germplasm from gene banks to their applied breeding programs. With the advent of new biotechnological techniques, this process of genetic manipulation is now being accelerated and carried out with more precision (neglecting environmental effects) and fast-track manner than the classical breeding techniques. It is also to note that gene banks look into several issues in order to improve levels of germplasm distribution and its utilization, duplication of plant identity, and access to database, for prebreeding activities. Since plant breeding research and cultivar development are integral components of improving food production, therefore, availability of and access to diverse genetic sources will ensure that the global food production network becomes more sustainable. The pros and cons of the basic and advanced statistical tools available for measuring genetic diversity are briefly discussed and their source links (mostly) were provided to get easy access; thus, it improves the understanding of tools and its practical applicability to the researchers.

Current agricultural and food systems encourage research and development on major crops, neglecting regionally important minor crops. Small millets include a group of small-seeded cereal crops of the grass family Poaceae. This includes finger millet, foxtail millet, proso millet, barnyard millet, kodo millet, little millet, teff, fonio, job's tears, guinea millet, and browntop millet. Small millets are an excellent choice to supplement major staple foods for crop and dietary diversity because of their diverse adaptation on marginal lands, less water requirement, lesser susceptibility to stresses, and nutritional superiority compared to major cereal staples. Growing interest among consumers about healthy diets together with climate-resilient features of small millets underline the necessity of directing more research and development towards these crops. Except for finger millet and foxtail millet, and to some extent proso millet and teff, other small millets have received minimal research attention in terms of development of genetic and genomic resources and breeding for yield enhancement. Considerable breeding efforts were made in finger millet and foxtail millet in India and China, respectively, proso millet in the United States of America, and teff in Ethiopia. So far, five genomes, namely foxtail millet, finger millet, proso millet, teff, and Japanese barnyard millet, have been sequenced, and genome of foxtail millet is the smallest (423-510 Mb) while the largest one is finger millet (1.5 Gb). Recent advances in phenotyping and genomics technologies, together with available germplasm diversity, could be utilized in small millets improvement. This review provides a comprehensive insight into the importance of small millets, the global status of their germplasm, diversity, promising germplasm resources, and breeding approaches (conventional and genomic approaches) to accelerate climate-resilient and nutrient-dense small millets for sustainable agriculture, environment, and healthy food systems.

2673ReseaRch M illets, which are comprised of a number of C 4 smallgrained, annual cereal grasses including barnyard millet, kodo millet, and little millet have abundant within-species racial diversity. These species also differ in ploidy levels. The ploidy levels in barnyard millet range from tetraploid to hexaploid to octaploid, while kodo and little millets are tetraploids (de Wet et al., 1983;Wanous, 1990). Barnyard millet has two distinct cultivated species, the Indian barnyard millet [E. colona (L.) Link] and Japanese barnyard millet [E. crus-galli (L.) Beauv], each with two Abbreviations: CB, culm branching; CR%, coincidence rate; CT, culm thickness; DF, days to 50% flowering; FL, fruit length; FLBL, flag leaf blade length; FLBW, flag leaf blade width; FLSL, flag leaf sheath length; FW, fruit width; G × E, genotype × environment; GH, growth habit; H´, Shannon-Weaver diversity index; IL, inflorescence length; LLR, length of lowest raceme; LRL, longest raceme length; MD%, mean difference percentage; NBT, number of basal tillers; NL, number of leaves; NNPAI, number of nodes on primary axis of inflorescence; NRAT, number of racemes above thumb; NRI, number of racemes per inflorescence; NSIB, number of secondary inflorescence branches; OPAS, overall plant aspects score; PE, panicle exsertion; PH, plant height; PL, peduncle length; PP, plant pigmentation; TL, thumb length; VD%, variance difference percentage; VR% variable rate.

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